Machine tool

ABSTRACT

A machine tool for machining workpieces ( 22 ), comprising three NC-controlled linear axes orthogonal to each other, namely a horizontal X-axis, a horizontal Y-axis and a vertical Z-axis, with a machine base ( 10 ), which comprises two vertically upwardly directed side beds ( 12 ) that are spaced from each other in the X-axis, with a bridge ( 28 ) displaceably guided in the Y-axis on top of the side beds ( 12 ), with a Z-slide disposed at the &amp;enter of the bridge ( 28 ) in relation to the side beds ( 12 ), which slide can be displaced in the Z-axis and carries a tool spindle ( 46 ), with an X-guide element ( 14 ) disposed on the machine base ( 10 ), with a wbrkpiece holder element ( 16, 18, 20 ) displaceable on the X-guide unit, and with a tool holder disposed on the tool spindle ( 46 ).

The invention relates to a machine tool for machining workpieces withthree NC-controlled linear axes orthogonal to each other.

When machining workpieces, particularly when performing fine machiningoperations in grinding machines, the shape of the workpieces to bemachined is taken into account by the number and configuration of thecontrolled axes. In the cylindrical grinding of rotation-symmetricalworkpieces, two linear axes are sufficient, as is true for simplegrinding machines, which two axes together with a rotative axis of theworkpiece and the rotating tool spindle can produce rotation-symmetricalcontours. For machining operations, particularly for grinding workpiecesthat are not configured rotation-symmetrically to the center line of theworkpiece, typically machine tools are used that have three linear axesorthogonal to each other, which position the tool spindle spatiallyrelative to the workpiece, and two rotative axes, which determine theposition of the tool, particularly of the grinding tool, at the toolengagement point in two additional angles of attack with respect to theworkpiece. In special cases, additionally a third rotative axis is usedfor producing free-form surfaces so as to reach the machining locationwith the main axes of the machine tool.

The technical complexity of the design of a machine tool of this typeincreases with the number of axes interacting with each other duringmachining. The linear axes must be oriented with utmost precision intheir orthogonality to each other and the rotative axes must be orientedwith utmost precision in their axial positions with respect to thelinear axes. Such precision can be maintained with the necessarytolerances when installing and adjusting the machine tool. It is moredifficult, however, to control deviations occurring during the operationof the machine tool. These deviations may be caused thermally as aresult of varying levels of heating of individual regions of the machinetool and also by deformations caused by different workpiece weights ormachining forces. Such errors can only be compensated for to a certaindegree by measurements and corrective action. Consequently, the resultsimprove the fewer the number of axes that are affected by operationalfactors. In particular, such compensation is possible when always thesame workpieces are being machined. As the number of axes increases andas they are used universally for different workpieces, such correctiveaction is hardly possible.

In known machine tools, typically the workpiece holder and the toolholder are connected to each other on one side and off-center by amachine tool table. Such a stand in principle responds to unilateralheating or loads by becoming deformed. For portal milling machines, suchas gantry machines, this situation is more favorable in that the tableconfiguration is provided on both sides of the machining space andsymmetrically to an extension of the machine tool. All three linear axesare disposed in a bridge carrying the tool spindle. While this bridge issupported symmetrically on both sides of the machining location, thetool spindle is displaceable in the bridge between the support points,so that this may again create asymmetrical weight and machining forces.Asymmetrical thermal load of the bridge, however, cannot be excluded.

From DE 42 12 175 A1 a lathe is known, wherein a machine base comprisestwo vertically upwardly directed side beds that are disposed at adistance from each other in the x-axis, on which cheeks a bridge isdisplaceable in the y-axis. On this bridge, the tool spindle can bedisplaced in the horizontal x-axis and the vertical z-axis by means of acompound slide. The tool is mounted stationary on the machine base. Theweight of the tool spindle and the workpiece as well as machining forcesact on the bridge asymmetrically in the Y-direction and their point ofattack on the bridge shifts in the X-direction during the machiningoperation.

It is therefore the object of the invention to create a machine tool formachining workpieces, wherein machining errors as a result of thermalinfluences and/or weight forces and machining forces are optimizedduring operation of the machine tool.

This object is achieved according to the invention by a machine toolwith the characteristics according to claim 1.

Advantageous embodiments of the invention are disclosed in the dependentclaims.

The machine tool according to the invention for the machining ofworkpieces is preferably configured as a grinding machine.

To minimize deformations due to thermal influences and weight andmachining forces, which result in errors, emphasis is placed on themachine tool according to the invention that both the design of themachine tool and the forces occurring during operation arecenter-symmetric to the extent possible. The tool spindle is provided ona bridge, which is displaceable in the Y-axis. In this bridge, the toolspindle is disposed center-symmetrically in relation to the X-axis. Thetool spindle is not displaceable in the X-axis, so that the spindlealways remains in this center location in the bridge. The X-axis formachining is configured as a workpiece support axis and provided on themachine base, on which the X-guiding unit for the workpiece holderelement is massively supported, so that the workpiece weight and themachining forces acting on the workpiece do not result in deformation.

If the machine tool, in addition to the three orthogonal linear axes, isalso provided with rotative axes, as is particularly advantageous foruniversal grinding machines, these rotative axes are disposed such thattheir impairment of the entire center symmetry of the machine tool isminimized.

A rotative axis, referred to as the C-axis, is configured to coincidewith the vertical Z-axis. The tool spindle can be rotated about thisC-axis with the spindle's axis intersecting the Z-axis so as to controland adjust the angle of attack of the tool in relation to the workpiece.

The rotating mount of the C-axis is integrated in the bridge, for whichpurpose the Z-slide in the bridge is mounted rotatably about thisC-axis. It is preferably if the Z-slide is vertically displaceable inthe C-axis and for symmetry reasons preferably coaxially in the centerof the C-axis. The mass of the rotative C-axis is reduced in that noseparate axis housing is required. The mass of the rotative C-axis alsodoes not have to be displaced vertically. The guide and the drive of theZ-slide can be rotated about the C-axis, so that the tool spindleprovided on the bottom of the Z-slide always maintains the same relativeposition to the Z-slide. A coaxially displaceable rotatable spindle isknown, for example, from DE 198 58 667 A1.

In an advantageous embodiment, apertures are provided in the side bedsof the machine base, through which apertures the X-guide provided on themachine base is guided. This way it is possible to provide a largetravel range in the X-axis, for example for workpieces extended in thisaxis, without having to increase the clearance in the X-direction forthe Y-guides carrying the bridge. The support of the bridge and toolspindle masses traveling on top of the side beds is distributedcenter-symmetrically among four columns, namely the two columns of eachside bed remaining on either side of the aperture. With this embodiment,the machine dimensions in the X-axis can be extended in accordance withthe respective machining task, without having to change the machinedesign.

So as not to apply asymmetrical load on the bridge in the Y-traveldirection, the Z-slide carrying the tool spindle is preferably disposedin the center of the bridge in relation to this Y-axis. As a result, nomoment of tilt occurs on the bridge and the Y-guide thereof, regardlessof the weight of the tool spindle and of the machining forces acting onthe tool spindle.

To be able to machine workpieces, which are rotation-symmetrical atleast to some extent and may be elongated in this rotational axis, arotative axis, referred to as the A-axis, is preferably configured tocoincide with the X-axis. This means that the workpiece in the workpiecechucking device can be rotated about this A-axis coinciding with thelinear X-axis. The respective area of the workpiece to be machined canbe rotated to face the machining tool by means of the A-axis.

The positioning of the workpiece in the X-axis guarantees that thismachining site is always positioned at the center of the machine toolbetween the side beds.

A third rotative axis can be implemented in that the tool spindle ismounted pivotably about a horizontal axis, referred to as the B-axis,which is provided in a plane orthogonal to the Z-axis.

It is preferable if the tool spindle is disposed in the Z-slide suchthat a tool chucked in the tool spindle is axially flush with the Z-axisand particularly with the rotative C-axis. As a result, the angle ofattack of the tool in the C-axis and optionally in the B-axis can bevaried, without causing the machining site, meaning the point of attackof the tool on the workpiece, to migrate from the center position of themachine tool.

It is advantageous to configure the machine base and the side beds asone piece in the form of mineral cast components. This guaranteessignificantly slower and more even thermal growth and high vibration ofthe machine base.

The invention will be explained in more detail hereinafter withreference to an exemplary embodiment illustrated in the drawing,wherein:

FIG. 1 is a front view of the machine tool, and

FIG. 2 is a vertically cut side view.

In the exemplary embodiment illustrated in the figures, a machine toolis illustrated, which is configured as a grinding machine.

The machine tool comprises a machine base 10, which extends in thedirection of the X-axis. At both ends of the machine base 10, which arespaced from each other in the X-direction, vertically upwardly directlyside beds 12 are provided, respectively. The machine base 10 and theside beds 12 are produced as one piece as mineral cast components.

At the top of the machine base 10, an X-guide unit 14 extendinghorizontally in the X-axis is mounted, which is supported across theentire length by the machine base 10. In the X-guide unit, a workpieceholder element is provided displaceably by NC-control in the X-axis. Theworkpiece holder element in the illustrated example substantiallycomprises a workpiece table 16 mounted displaceably on the X-guideelement 14, on which table a workpiece chucking element 18 and atailstock 20 are provided. A workpiece 22 can be chucked in theworkpiece chucking element 18 in an axis extending the X-direction andis supported at the opposite end by the tailstock. The workpiecechucking element 18 comprises a rotary drive, which is referred to asthe A-axis, by means of which the workpiece 22 can be rotated in anNC-controlled manner about its axis parallel to the X-axis.

The two side beds 12 comprise an aperture 24 in their lower regionsconnecting to the machine base 10. The apertures 24 are flush with theX-guide element 14 and are configured symmetrically to the X-guide inthe horizontal Y-direction perpendicular to the X-axis. The X-guideelement may extend through the apertures 24, so that also workpieces 22elongated in the X-direction can be received in the workpiece holderelement and guided through the apertures 24, the linear displacementpath of which is larger in the X-direction than the inside clearance ofthe side cheeks 12.

On the upper horizontal boundary surfaces of the side beds 12 extendingin the Y-direction, Y-guides 26 are provided. A bridge 28 that isdisplaceable in the Y-axis is mounted in these Y-guides 26. The bridge28 spans the inside of the machine tool between the side beds 12 in theX-direction and then strengthens the side beds 12 at the free upperedges thereof towards each other in the X-direction. The bridge 28 canbe displaced by NC-control in the Y-axis by means of a driving motor 32disposed on a machine back wall 30 and by means of a spindle 34.

At the center of the region, meaning both in relation to the X-directionand in relation to the Y-direction, a Z-slide 36 is provided at thecenter of the bridge 28. The Z-slide 36 is guided in a sleeve 38 in,thevertical Z-axis. In the sleeve 38, the Z-slide can be displacedvertically by NC-control by means of a driving motor 40 and a spindle42. The sleeve 38 is not displaceable axially in the bridge 28 and canbe rotated about a vertical axis by NC-control. This vertical axis ofrotation of the sleeve 38, referred to as the C-axis, coincides with theZ-axis.

On the end of the Z-slide protruding toward the bottom out of the sleeve38 and the bridge 28, a radially projecting bracket 44 is mounted. Onthis bracket 44, a tool spindle 46 is pivotably mounted by means of apivot joint 48. The pivot axis of the pivot joint 48 extends off-centerfrom the Z-axis and/or the C-axis in a horizontal plane orthogonal tothe Z-axis. The pivot axis of the pivot joint 48 forms a third rotativeaxis, referred to as the B-axis.

The tool spindle 46 is driven by a coaxial spindle motor 50 and at theend thereof comprises a tool holder, in which a tool 52, in theillustrated example a grinding tool, can be chucked.

For the grinding operation of the workpiece 22, the workpiece ispositioned in the X-axis by means of the workpiece holder device,wherein the respective location of the workpiece 22 to be machined ispositioned in the X-axis at the center between the side beds 12. Themachining tool 52 is positioned by means of the movement of the bridge28 in the Y-axis and by means of the movement of the Z-slide 36 in theZ-axis. By rotating the workpiece 22 about the A-axis, the scope of theworkpiece 22 to be machined is positioned to face the tool 52. Byrotating the sleeve 38 about the C-axis, the axis of the tool spindle 46and hence that of the tool 52 is positioned in the X-Y plane. Bypivoting the tool spindle 46 about the B-axis of the pivot joint 48,furthermore the angle of inclination of the tool spindle 46 and thusthat of the tool 52 in relation to the X-Y plane can be adjusted. Bydisposing the pivot joint 48 and the fastening for the tool spindle 46outside the Z-axis, the tool 52 and hence the machining location on theworkpiece 22 are flush in the Z-axis and/or the C-axis, regardless ofthe rotation of the tool spindle 46 about the C-axis. The clearance ofthe side beds 12 in the X-direction allows a rotation of thehorizontally disposed tool spindle 46 about the C-axis by 360°.

REFERENCE LIST

10 machine base 12 side beds 14 X-guide unit 16 workpiece table 18workpiece chucking element 20 tailstock 22 workpiece 24 aperture 26Y-guide 28 bridge 30 machine back wall 32 driving motor 34 spindle 36Z-slide 38 sleeve 40 driving motor 42 spindle 44 bracket 46 tool spindle48 pivot joint 50 spindle motor 52 tool.

1. A machine tool for machining workpieces (22), comprising threeNC-controlled linear axes orthogonal to each other, namely a horizontalX-axis, a horizontal Y-axis and a vertical Z-axis, with a machine base(10), which comprises two vertically upwardly directed side beds (12)that are spaced from each other in the X-axis, with a bridge (28)displaceably guided in the Y-axis on top of the side beds (12), with aZ-slide disposed at the center of the bridge (28) in relation to theside beds (12), which slide can be displaced in the Z-axis and carries atool spindle (46), with an X-guide element (14) disposed on the machinebase (10), with a workpiece holder element (16, 18, 20) displaceable onthe X-guide unit, and with a tool holder disposed on the tool spindle(46), characterized in that the axis of the tool spindle (46) intersectsthe Z-axis and that the tool spindle (46) can be rotated by NC-controlabout an axis (C-axis) coinciding with the Z-axis, for which purpose theZ-slide (36) is mounted in the bridge (28) rotatably about this C-axis.2. The machine tool according to claim 1, characterized in that the sidebeds (12) each comprise an aperture (24), through which the X-guideelement (14) is guided.
 3. The machine tool according to claim 1,characterized in that the Z-slide is disposed in the center of thebridge (28) also in relation to the Y-axis.
 4. A machine tool accordingto claim 1, characterized in that the workpiece (22) can be rotatedabout an A-axis coinciding with the X-axis by NC-control in theworkpiece holder device (16, 18, 20).
 5. A machine tool according toclaim 1, characterized in that the tool spindle (46) is mountedpivotably about a horizontal B-axis, which is located in a planeorthogonal to the Z-axis.
 6. A machine tool according to claim 1,characterized in that a tool (52) chucked in the tool holder of the toolspindle (46) is located substantially in the Z-axis.
 7. The machine toolaccording to claim 6, characterized in that the clearance of the sidebeds (12) in the X-direction allows a rotation of the tool spindle aboutthe C-axis by 360°.
 8. A machine tool according to claim 1,characterized in that a machine base (10) and the side beds (12) form asingle-piece mineral cast component.
 9. A machine tool according toclaim 1, characterized in that the machine tool is configured as agrinding machine.